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Analysis:
A. 3.07g/63.546 amu =0.0483 mol <-1.
0.0483 mol *6.022*1023=2.91*1022 atoms Cu. <-2.
B. 0.72g/20=0.036g 0.036g/(1.00794+15.9994)=0.0021 mol <-1.
0.0021 mol *6.022*1023=1.26*1021 molecules <-2.
C. 6.49/[2(12.0107)+3(1.00794)]=0.104 mol PVC <-1.
0.104*6.022*1023=6.26*1022 molecules <-2.
6.26*1022*2=1.25*1023 carbon atoms <-3.
6.26*1022*3=1.88*1023 hydrogen atoms <-4.
D. 3.61g/(8*12.0107+8*1.00794)=0.0347 mol <-1.
0.0347*6.022*1023=2.090 molecules
2.090*(8+8)=3.34 atoms
Conclusion:
Avogadro's number links the amount of atoms or molecules in a substance to the mole. the molar mass is used to convert between mass of a substance and the mole. {mole}={number of atoms or molecules}/{Avogadro's number} {mole}={mass(g)}/{molar mass(amu)} {atoms}={molecules}*{atoms per molecules} {molecule}={moles}*{Avogadro's number}. Molecules are made of atoms.